If your dog is raising his paw as he would to shake hands, then it is a show of affection and a request for continued attention. If he's standing and putting his paws on your shoulders, then he's making a subtle move for dominance by making himself "taller" than you.

Your dog puts his paws on you when you are petting him as a way to show his affection. Think of it almost as if he was hugging you. He;s letting you know it makes him happy when you pet him. It is also a way from him to get and keep your attention.